China’s biggest internet companies got that way with at least tacit support from the government. Now two events have raised doubts about where those giants stand: the last-minute suspension of a stock offering by billionaire Jack Ma’s sprawling Ant Group Co. due to regulatory pressure; and the introduction of a draft antitrust policy seemingly designed to rein in the most powerful, including Alibaba Group Holding Ltd. (Ant’s major backer) and Tencent Holdings Ltd., operator of the WeChat super-a